Patent GB-746741-A (GB)
Title: Improvements in and relating to electric signalling systems
Inventor: ROBIN HAROLD KILNER
IPC: H04L5/26
Filed: 1949-12-14
Abstract: 746,741. Type-printing telegraphy; distributer systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Dec. 6, 1950 [Dec. 14, 1949], No. 32126/49. Class 40 (3). [Also in Group XL (c)] In an electrical signalling system, such as a teleprinter system or a pulse code modulation system, in which characters, or samples of the amplitude of a wave, respectively are transmitted by the selection of pulses from a group of pulses, means responsive to each of said selections operates to generate a burst of oscillations, the frequencies of the oscillations in successive bursts being related to, or determined by, successive selections. Each selection may give rise to a predetermined frequency, or the frequency for a selection may be dependent upon the immediately previous selection. As applied to a multi-channel teleprinter system, Fig. 1a, comprising fifteen tape transmitters A1 ... A15, a distributer D2 rotating at six revolutions per second causes the tapes to be sensed in succession and impulses to be applied selectively to terminals T1 ... T5, a secorid distributer D1 energizing coils L1 ... L15 in succession to step the tapes in the associated transmitters. A frequency generator comprises a wheel W rotated at 30 revs. per second and formed with thirty-two rings of apertures AP, providing thirty-two different frequencies, and connected to a multi-core cable CA leading to a multi-gate circuit G6 having an output terminal T8. Three equallyspaced apertures AP1 on the wheel W provide a train of 90 impulses per second and these are applied over terminal T6 to a Kipp relay K2 having a variable delay control. The output of the relay K2 is fed to buffer circuits B1 ... B5 and to a second Kipp relay K1 which jointly controls the gating circuits G 1 ... G5. Five flip-flop circuits F1 ... F5 are controlled jointly by the buffer circuits B1 ... B5 and by the selection of impulses applied to the terminals T1 ... T5 to effect through a matrix GM of germanium rectifiers the opening of a gate in the assembly G6 so that a corresponding frequency is passed to the terminal T8, a limiter and phase splitter LP, a selected one of four flip-flops F6 ... F9 performing a frequency division depending on the portion of a switch SW1. The oscillations are modulated at MD with 90 c/s oscillation applied at the terminal T7 and derived from a generator ACG on the shaft of the motor M1 and wheel W, Fig. 1b. The output of the cathode follower CF1 is passed to a transmitter TR where the 90 c/s modulation is removed, and the demodulated tones applied to obtain frequency shift of a carrier which is multiplied to obtain the original modulating or signal frequencies and the 90 c/s modulation re-applied. At the receiver, the incoming modulation is applied from terminals T9, T10 to a transformer N2, attenuator IC1, amplifier AMP1 and two phase-changing devices PC1, PC2 alternating the phase of the incoming oscillations by 45 degrees. These phase-displaced oscillations are applied to a pulseforming circuit PF1 generating two trains of impulses at twice the frequency of the applied oscillations, and relatively displaced by 90 degrees-the positively displaced pulses being termed "working pulses" and applied through a cathode follower CF2 to a terminal T11 and the other pulses termed "timing pulses" being applied through a cathode follower to a terminal T12. An output is also taken from terminal T13 and the 90-cycle modulation abstracted to control the synchronizing circuit SC. A tuning-fork TF2 produces oscillations at 1800 c/s which are passed to a synchronizing control circuit SC producing pulses at 3600 per second passed to two flip-flops F10, F11, giving rise to impulses at 900 per second which are applied to a decade ring DR comprising flip-flops 1 to 10 so that the counter DR completes its cycle 90 times per second, or once in 11.11 milliseconds. An output from the first flip-flop is taken via buffer stage B11 to a terminal T14 and from flip-flops 7, 8, 9 to terminals T15, T16, T17. Outputs are also taken from flip-flops 1, 3, 5, 8 to a terminal T18. The terminal T14 is connected to one input terminal of a flip-flop F12, and the timing impulses from terminal T12, Fig. 2a, are fed to a gate G7. The output terminal of G7 is connected to the other input terminal of F12. Each time a pulse appears at T14, i.e. every 11.11 milliseconds, F12 is switched in and opens gate G7. The next timing pulse at T12 passes to the flip-flop F12 and switches it off. When F12 is switched off it closes the gate G7 and switches on a further flip-flop F13 which applies a pulse to a terminal T19 and to a terminal T20 of a timing device CLC which provides a pulse at T21 5.55 milliseconds after the impulse applied to the terminal T20. The output pulse at T21 is applied to F13 to cut it off and the voltage at T19 is in the form of an oscillation of square waveform, each halfcycle lasting 5.55 milliseconds and beginning and ending midway between the working pulses. The timing device CLC comprises a crystal-controlled oscillator with a number of frequency division circuits so that a pulse is provided at a time 5.55 milliseconds after a pulse is applied to a gate to control a number of flip-flops. The working pulses from the terminal T11 are applied to a gate G9 which is opened and closed for periods of 5.55 seconds by the oscillation of square waveform from the terminal T19. As the "timing" pulses are delayed 90 degrees relative to the " working " pulses each cycle of the square wave oscillation commences between two "working" pulses, and the synchronizing circuit SC is arranged to ensure that the gate G9 opens at about 2.77 millisecond after each burst of oscillations is applied to the terminals T9, T10. The " working " pulses are applied to a five-digit binary counter comprising five two-state flipflop circuits F24 ... F28 so that each of the circuits is operated from a preceding circuit, the arrangement being such that the number of impulses received during. a period of 5.55 milliseconds evaluates the frequency and determines the condition of the respective flip-flops F24 ... F28 in accordance with the flip-flops F1 ... F5 of Fig. 1. About 1.11 milliseconds after the end of the 5.55 millisecond period, a pulse at terminal T15 operates flip-flop F29 so that the gates G10 ... G14 are opened and the respective impulses determined by the flip-flops F24 ... F28 are applied to terminals T22 ... T26. After a further 1.11 milliseconds an impulse at T16 switches off flip-flop F29 which closes gates G10 ... G14 and switches on flip-flop F30 which switches off the flip-flop circuits F24 ... F28. About 1.11 milliseconds later, a pulse at T17 switches off flip-flop F30 so that the binary counter and its control circuits are returned to normal to start the next count. Distributer arrangements. The signal elements applied to the terminals T22 ... T26 are lengthened for operation of the teleprinter allocated to the various channels by a commutator arrangement comprising insulated segments C1 ... C15, brushes BR1 and BR2 engaging contiguous segments and a ring SL1 at positive potential of, say, 100 volts and a further brush BR3 connecting the segments to an outer ring SL2 at a negative potential of, say, 100 volts. The commutator arrangement is rotated at six revolutions per second by reduction gearing of a 5 : 1 ratio coupled to a motor M2 driven from a counter CR fed with pulses from the terminal T18, Fig. 2b, delivering 360 pulses per second, the counter having a rotational frequency of 60 cycles per second. The distributing arrangement comprises seven thyratrons GT1 ... GT7 such that the valves strike solely when the anode voltage is positive in addition to positive voltage on the two grids. When, for example, the brush BR3 is on contact C15 and the brushes BR1, BR2 are on contacts C1, C2 a negative pulse is applied for 11.11 seconds to the grid of V1 so that this valve cuts off and applies a positive voltage to the inner grids of the valves GT1 ... GT7. The outer grids of the valves GT1 ... GT7 are selectively made positive according to the impulses applied by the flip-flops of the binary counter. The valves GT6, GT7 are triggered since they also have positive potential on their anodes and outer grids, but the currents through the windings of the relay REL1 are equal so that the relay remains in its space condition. The brushes BR1, BR2 are respectively on segments C2, C1, and the impulses from the terminals T22 ... T26 render valves GT1 ... GT5 selectively conducting, but equal currents pass through the windings of the relay REL1. As the brushes move over the segments C3 ... the valves which are conducting pass increased current for periods of two segments, i.e. for 22 milliseconds. After the transmission of the five selecting impulses, the brushes BR1, BR2 apply the additional positive potential to the valves GT6, GT7 for a period of three segments, i.e. for 33 milliseconds, so that a mark (stop signal) of that duration is applied to the relay REL1 and over the terminal T30 to its associated teleprinter. During the passage over the final segment of the complete revolution the additional potential is removed from the valves GT6, GT7 so that for a duration of 11.11 milliseconds a spacing element is fed to the terminal T30. A similar distributer arrangement is provided for each channel, the triodes, such as V1, being operated in sequence by reason of connection to successive segments of the associated distributer member, Fig. 2f. The system is set up in correct channel relation by transmitting a predetermined frequency, e.g. 1800 c.p.s. over the channel appertaining to the first transmitter and a different frequency over the remaining channels. At the receiver, Fig. 2a, a switch SW2 is moved to its lower position in which a frequency of 1800 c.p.s. from a local source is fed via a transformer N2 to the receiver circuit to maintain the drivin